Plug-in bushings of the type mentioned initially are described, for example, in GB 689 560, DE 10 2007 022 641 A1 and in an article by Klein et al. “A New Separable 170 kV Outdoor Bushing System Creates a Multi-Purpose Transformer or Switchgear”, Kontaktsysteme GmbH & Co. KG (2006). The described plug bushings each have a plug part which can be inserted into a mating plug part, which is fitted to the transformer forming a seal for the insulating agent, while the transformer is being installed at the installation location. This considerably simplifies transport and maintenance of the transformer.
During insertion of the bushing, a joint is formed between an insulating sleeve of the mating plug part and the plug part, which is generally in the form of a plug, of the bushing, which joint is subject to the effect of a strong electrical field during operation of the transformer and of the bushing, and which can be dielectrically strengthened for example with the aid of insulating oil (GB 689 560), with the aid of a field control device which is integrated in the bushing, and by using an elastomer which bounds the joint.